"He repeats. He's so consistent with his delivery, his arm action, his arm slot, release point, it's tough to see what is coming out," Seattle manager Eric Wedge said. "That's what you have to do. If you're going to be a solid starting pitcher up here, you've got to do that."

Iwakuma (4-1) took a one-hitter into the sixth inning before running into trouble, putting together another strong outing to help cement himself and Felix Hernandez as one of the top rotation duos in baseball. Iwakuma has allowed five earned runs over his past five starts, and the number could have been even smaller if not for a scoring change that ended up tagging him with two earned runs against the A's.

Overshadowed by Hernandez, the ace of the Mariners staff, Iwakuma has been nearly as solid this season. He's pitched at least six innings in seven of eight starts despite being bothered by a lingering blister on his pitching hand, and has not allowed more than three earned runs in any start.

"Those two have just been on another level," Seattle third baseman Kyle Seager said. "Everybody knows Felix, obviously, but (Iwakuma) he's been flying under the radar a little bit but he's been just as impressive. It's been pretty fun to play behind those two especially."

Iwakuma gave up a solid leadoff single to right field to John Jaso and then was unhittable for the next five innings. He set down 15 straight with remarkable ease, through a combination of broken bats, weak ground balls and lazy flies. He struck out Yoenis Cespedes to close the first, struck out Derek Norris and Jaso in the third and retired Josh Donaldson and Daric Barton swinging to end the fifth.

Iwakuma's streak finally ended at 16 straight retired when Eric Sogard reached on an infield single -- originally ruled an error -- with one-out in the sixth inning. His ground ball bounced off the arm of shortstop Brendan Ryan and Sogard reached without a throw. Jaso followed with a bloop single, and the A's finally got to Iwakuma on Jed Lowrie's two-out, two-run double into the right-field corner. Lowrie had just one RBI in his previous 17 games before the double.

The scoring change cost Iwakuma a chance to have his ERA dip below Hernandez's for the best in the American League. Instead, Iwakuma's ERA rose from 1.61 to 1.74. He gave up four hits, struck out nine and walked none. Tom Wilhelmsen pitched the ninth for his 10th save.

"It's a mental relief, being able to pitch with that much of a big lead is big for myself, so being able to pitch with a better rhythm helped me be able to go through seven innings," Iwakuma said through an interpreter.

Seattle scored twice in the first off Oakland starter Dan Straily (1-1). Seattle broke the game open with Ibanez's three-run homer in the third inning that came with two outs. Oakland lost its season-high fifth straight and dipped below .500 since starting the season 1-2. The A's fell to 2-6 on their current 10-game road trip and only once has Oakland scored more than three runs.

"Everybody has to pick everybody up and we're not doing that right now," Oakland manager Bob Melvin said.

Straily struggled to get through five innings, but didn't get help from his defense starting in the first inning that led to two runs. Kendrys Morales' chopper to left side bounced past both third baseman Josh Donaldson and Lowrie at shortstop to put runners at the corners with one out instead of a possible inning-ending double play. Michael Morse followed with an RBI single and Justin Smoak lined an RBI double to give Iwakuma an early lead.

Seattle's runs in the third also came thanks to a fortunate bounce. Seager reached on an infield single that spun awkwardly off the end of his bat. Straily gave up a two-out walk to Smoak that proved costly when Ibanez turned on a 1-1 pitch for his third homer of the season and first since April 14.

"It's always nice to contribute and the last few games I've played I guess have been better," Ibanez said.

Game notes
Seattle improved to 16-8 this season when its starting pitcher works at least six innings. They are 1-11 when the starter fails to get through six. ... Seager scored three of the four times he reached base. ... Oakland's Derek Norris hit a solo homer, his first of the season, in the eighth off Seattle reliever Oliver Perez.